Ablation of myocardial tissue is well known as a treatment for cardiac arrhythmias. In radio-frequency (RF) ablation, for example a catheter is inserted into the heart and brought into contact with tissue at a target location. RF energy is then applied through electrodes on the catheter in order to create a lesion for the purpose of breaking arrhythmogenic current paths in the tissue. Specifically, atrial fibrillation is an abnormal heart rhythm originating in the atria (top chambers of the heart). Instead of the impulse traveling in an orderly fashion through the heart, many impulses begin and spread through the atria, causing a rapid and disorganized heartbeat. Ablation of the four pulmonary veins, also known as “Pulmonary Vein Isolation” (PVI), using a circumferential mapping technique is proving to be successful for many patients with atrial fibrillation.
The ablation is performed by delivering energy from a catheter to the area of the atria that connects to the pulmonary vein ostia, producing a circular scar or lesion around the ostium.
The lesion then blocks any impulses firing from within the pulmonary vein, thus preventing atrial fibrillation from occurring. The process is typically repeated to all four pulmonary veins.
Ablation has been accomplished primarily by means of focal ablation, that is, ablation by a tip electrode at a distal end of the catheter. Thus, for linear ablation along a line or curve, the tip electrode is repositioned repeatedly or dragged across the tissue along the line or curve during a prolonged ablation. Repositioning or dragging is time-consuming and proper tissue contact is often difficult to achieve when maneuvering in the small confines of the atria. Also known are irrigated ablation tip and ring electrodes which are effective at reducing electrode temperature during ablation to minimize the formation of char and coagulum. However, fluid load on the patient is a concern, especially where multiple electrodes are being irrigated.
Accordingly, there is a desire for a catheter adapted for PVI procedures regardless of ostium shape or size that would improve catheter maneuverability and targeting of the ostia which would in turn improve lesion formation and shorten duration of ablation procedures. In particular, there is a desire for a catheter with multiple ring electrodes that can ensure greater and more stable tissue contact with the ostium by enabling two simultaneous contact locations between the ring electrodes and the ostium.